supplement MEM with phenol-red??? - (Apr/19/2009 )

Dears
I just have received MEM media but I superised when I see its color is colorless that means I have to supplement it with phenol red....it is 100ml (1000X) so how much of phenol red should be addad and should I resterilize the media after adding phenol red and recheck the pH????

Any help??

You don't have to add phenol red. Phenol red is just a pH indicator that has the minor advantage of making it easier to tell you when to split your cells. However, you should never rely on phenol red for this as the pH of the solution can be affected by many things including the %CO₂ in your incubator, presence of a bacterial of fungal contamination. What you should be doing is inspecting your cells daily and looking at how frequently you passage your cells and growth rates etc.

If you do decide to supplement, and you definitely don't have to: a 100X solution is diluted 1 part in 100, i.e. 1 ml with 99ml diluent. If both solutions are sterile and you are careful with your technique, you can add one to the other, as you would for FCS/FBS into medium. If you need to sterilise, you will have to filter through a 0.2 um filter.

Thank you somuch

I should also add - phenol red is a weak estrogen analogue, if your cells express estrogen receptor (most breast cell lines do, but it isn't restricted to them), then you shouldn't use phenol red in the culture.